Elementary Surveying

Elementary Surveying

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This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1842 edition. Excerpt: ...plates together. Now turn the instrument on its axis, until the marked end of the needle settles exactly at the division in the compass box at N, or north, marked 360 or 180, and tighten the clamping screw, A; then, if the needle does not accurately agree with the 360 or 180 (as the case may be, for theodolites are differently numbered, ) in the compass box, use the micrometer or tangent screw, B, which will adjust it to the greatest nicety. All is now ready to take a bearing. Place a staff or bandrol at the point B, where the road makes a bend, and examine your instrument again to see, 1 st, that the index or zero of the vernier corresponds with zero of the horizontal circle; 2nd, that this circle is truly level; 3rd, that the needle points exactly to the division at N; and, lastly, that the clamping screw is firm. To take the bearing of the staff planted at B, loosen the screw, P, which connects the vernier plate with the horizontal circle, and turn the vernier plate, with the upper portion of the theodolite, on its axis; continue this until the staff at B is seen through the telescope: then tighten P, and turn the micrometer screw, N, at the same time, raising or depressing the telescope as much as may be requisite. Fix the intersection of the hairs in the telescope precisely on the bottom of the staff at B. The divisions in the compass box will indicate how many degrees have passed the stationary needle; but we must refer to the vernier for the exact measure of the angle, that a line from A to B forms with the meridian, which meridian is represented by the direction of the needle. On examination, we find that the zero of the vernier is something past the 50th degree of the circle; and looking along the vernier, through the magnifying glass, it..show more

Product details

  • Paperback | 44 pages
  • 189 x 246 x 2mm | 95g
  • Rarebooksclub.com
  • Miami Fl, United States
  • English
  • black & white illustrations
  • 1236537467
  • 9781236537461